Abstracts

Vigabatrin is used for treatment of partial and secondary generalized seizures and infantile spasms in Europe and Asia. A number of studies have shown that vigabatrin causes visual field defects. Many of these patients are asymptomatic. There are difficulties in assessing these patients with conventional visual fields due to poor compliance and reproducibility. The wide field multifocal electroretinogram (WF-mfERG) offers an objective test with improved spatial and temporal resolution over conventional visual fields and has been shown to be able to detect retinal pathology reliably. A long term longitudinal study is being undertaken at the Epilepsy Unit, Western Infirmary, Glasgow to objectively assess the progression of neuro-retinal toxicity associated with vigabatrin. Ten patients with localization-related epilepsy who have been taking vigabatrin for at least 6 years have been reassessed. These patients underwent WF-mf ERG as well as logMar visual acuity, colour vision assessment, static perimetry and ERG (global retinal function) and these tests were repeated after two years. All patients underwent brain MRI, those with intracranial pathology affecting the visual pathway were excluded. Ten control patients who were matched for age, sex, duration of epilepsy and seizure control were also included. First order parameters namely the P1 and N1 amplitude and latency were measured. The WF-mf ERG showed a significant increase in P1 latency in three out of the 10 patients. There was no change in either the vigabatrin group or control group in visual fields, visual acuity or colour vision within the two year follow up period. One out of these three patients had previous normal wide field multifocal parameters. The significant increase in P1 latency indicates progression of neuro-retinal toxicity. The Wide Field multifocal ERG is possibly more sensitive and specific than conventional methods of visual function testing in assessing patients on vigabatrin with progressive induced neuro-retinal toxicity. (Supported by Chief Scientist Office. Grant #CZB/4/78)